Neoproterozoic glaciations are widely thought to have encased the Earth in ice until their termination, i.e., the Snowball Earth hypothesis, with profound implications for the evolution of landscapes and life. However, the extent of sea and land ice remains uncertain owing to incomplete Earth system models and inappropriate simulation methods. Here we simulate the full life cycle of a Neoproterozoic glaciation, from initiation to deglaciation, using a comprehensive Earth system model with an energy-conserving surface mass balance scheme. We show that only a fully sea-ice-covered ocean can reconcile geological evidence for tropical land ice. The extremely weak hydrological cycle resulting from a completely ice-covered ocean allows ice-free areas to persist on land and keeps most ice sheets thinner than one kilometer. As atmospheric CO₂ accumulates, the ice-free area and hydrological intensity increase and undergo an abrupt transition during the mid-glacial period. Our results indicate that Neoproterozoic glaciations exerted limited surface erosion. The extreme environment of a fully ice-covered ocean and exposed land caused widespread extinction and may have promoted terrestrialization, shaping a distinctive evolutionary trajectory. These findings reshape the classic Snowball Earth picture and provide new insights into the impacts of this extreme climate event on Earth and life.
 

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